Manufacturing containers of thermoplastic material by forming preforms, for example by blow molding or by stretch blow molding, is known. To perform the forming operation, it is necessary to heat the body of the preforms beforehand to a glass transition temperature so as to render it malleable. The installations for mass production of containers have for this purpose stations for heating preforms.
A blow molding station generally has the shape of a tunnel in which at least one of the walls is formed by an assembly of several heating modules such as the one described above. The preforms advance along the tunnel in front of the heating modules while rotating around themselves so that their body is uniformly heated to a temperature that is suitable for the forming operation.
The lamps used for the heating of the preforms are generally halogen-type lamps that emit a heating electromagnetic radiation, for example an infrared radiation. They comprise a tubular portion of the bulb that contains a filament that extends longitudinally between two end caps. Each end cap makes possible the supplying of electricity to the filament. When it is supplied with the adequate electrical power, the filament emits the heating radiation radially in all directions.
Furthermore, for the forming of certain container types of thermoplastic material, it is preferable to heat certain areas of the preform to very precise temperatures. To make it possible to heat selectively certain areas of the preform, it is known to insert an optical lens on the path of the beam. Such a solution is described in greater detail in the document EP-B1-0,820,376. The lens makes it possible to focus the heating radiation in a precise area of the preform and thus to avoid the heating of certain areas of the preform such as the neck.
The lens is generally fastened to the tubular portion of the bulb by means of fastening brackets. For example, they are collars that are tightened around the emissive portion of the lamp.
Nevertheless, the fastening brackets then make a shadow by preventing a portion of the heating radiation from reaching the preforms.
To improve the efficiency of these lamps, it is known to arrange reflecting means to redirect the radiation toward the preform. To do this, it is known to arrange a reflector behind the lamp. Such a design is, for example, described in the document WO-A1-2011/039667.
However, in this configuration, the space reserved between the reflector and the tubular portion of the bulb is insufficient to admit the fastening brackets of the lens.